In order to move toward a comprehensive analysis of the macroeconomic dimensions of the impact of migration upon development, it is proposed here to build a large-scale computer simulation model of the Colombian economy which emphasizes those variables and those relationships relevant to migration flows. It will be distinct from previous models of the Colombian economy and all previous models of less-developed economies in at least six ways. First, it will be the first large scale model designed primarily for analysis of migration phenomena anywhere. Second, it will be the first model of the Colombian economy designed to simulate disequilibrium phenomena such as urban unemployment, persistent wage differentials, and migration flows which do not respond instantaneously to theoretical stimuli. Third, the specification and estimation of the model will involve testing of several new relationships between migration and development which have not been evaluated previously. For example, it will be hypothesized that both actual migration flows and the impact of those flows upon rates of population increase have measurable significance for aggregate savings rates. Furthermore, detailed analysis of the "urban transformation costs" of migration, both increases or decreases in the costs of providing basic services and the changes in quantity and quality of basic services, will be undertaken and incorporated into the model. Finally, estimates of changes in average labor productivity associated with movement from rural or small town setting to larger-city setting will be derived and incorporated. The model will also be designed so that the four or five most feasible potential policies for affecting rates of migration may be tested, compared, and evaluated.